1. Field of the Invention
This invention relates to electric lamps and has particular reference to a compact fluorescent lamp unit that is adapted for use as a direct replacement for incandescent type lamps in lighting fixtures employed for residential and commercial illumination.
2. Description of the Prior Art
Fluorescent lamp units having integral circuit and base components which permit the unit to be screwed into and operated in the sockets of lighting fixtures that are designed for incandescent type lamps are generally well known in the art. A lamp unit of this type having a cylindrical envelope that contains concentric annular partitions (or which is made from tubing that is bent upon itself to provide a U-shaped bulb) is disclosed in U.S. Pat. No. 3,551,736 granted Dec. 29, 1970 to Doehner. As disclosed in FIG. 5 and at lines 24-30, column 2 of this patent, if a tubular U-shaped bulb is used as the envelope it may be additionally twisted into spiral shape or redoubled on itself to provide a generally M-shaped envelope. A lamp assembly having adapter means which accommodates a conventional straight tubular fluorescent lamp and contains a ballast transformer that is part of a threaded base member which permits the lamp assembly to be screwed into an incandescent lamp socket is disclosed in U.S. Pat. No. 3,815,080 granted June 4, 1974 to F. Summa.
According to a more recent development, a screw-in type fluorescent lamp bulb is provided with integral ballast means that is disposed in telescoped relationship with an envelope that defines a discharge space of flat toroidal shape of similar configuration. A lamp unit of this type is disclosed in U.S. Pat. No. 3,953,761 granted Apr. 27, 1976 to T. Giudice. Another fluorescent lamp assembly of this general type having a tapered cylindrical envelope of molded glass that defines a helical-shaped discharge channel and accommodates a ballast component is described in U.S. Pat. No. 3,899,712 issued Aug. 12, 1975 to H. Witting.
An electrodeless fluorescent lamp unit of the screw-in type that is energized by high frequency energy produced by a self-contained radio-frequency oscillator and ferrite core is disclosed in U.S. Pat. No. 3,521,120 granted July 21, 1970 to J. M. Anderson.
Electric discharge lamps having tubular envelopes which are bent into various shapes to provide concentrated sources of light are also generally well known in the art. A sodium-vapor discharge lamp of double-ended construction having an envelope formed from a vitreous tube that is folded or bent upon itself twice to provide three straight segments that are disposed in triangular-spaced relationship is disclosed in British Pat. No. 854,745 published Nov. 23, 1960 (FIGS. 3 and 4 embodiment). A luminous discharge tube designed for advertising and display purposes (of for use as a beacon light) and having thimble-like electrodes and an envelope which is formed from glass tubing bent upon itself eleven times to provide a corresponding number of conjoined U-shaped sections is disclosed in U.S. Pat. No. 1,898,615 granted Feb. 21, 1933 to Byrnes. A plug-in type discharge lamp having a tubular envelope that is bent upon itself three times to provide a multi-segment envelope which is disposed within a heat-conserving double-walled enclosure is disclosed in U.S. Pat. Nos. 2,001,511 and 2,200,940 granted to Uyterhoeven et al.
Fluorescent lamps having "three-dimensional" type envelopes that are formed by coupling several arcuate lamp components together or interconnecting several straight tubular bulbs in "bundled" configuration are also known in the art and are disclosed in U.S. Pat. No. 2,652,483 (Laidig et al.) and U.S. Pat. No. 3,501,662 (Plagge), respectively.